Winsock

Winsock, short for Windows Sockets, is the Windows API that enables software running on Microsoft Windows to access network services using the Berkeley sockets interface. It provides a standard set of socket-level functions for creating, configuring, and using both stream-oriented (TCP) and datagram (UDP) sockets, as well as facilities for address and name resolution and asynchronous I/O. The API is exposed to applications through the Ws2_32.dll library and sits between user-mode software and the Windows networking stack.

History and scope: Winsock originated in the early 1990s as Winsock 1.x and was followed by Winsock 2 in the late 1990s. Winsock 2 added IPv6 support, a more flexible provider model, enhanced name-resolution routines (getaddrinfo, getnameinfo), and improved asynchronous I/O and performance. A Layered Service Provider mechanism allowed software to intercept or extend Winsock calls, though newer Windows versions emphasize built-in capabilities and alternative extensibility methods.

Programming model: Applications initialize the API with WSAStartup to request a version, then create sockets with socket(), and use bind(), listen(), and accept() for servers or connect() for clients. Data transfer uses send/recv or their datagram counterparts sendto/recvfrom, and sockets are closed with closesocket. For name resolution, getaddrinfo and getnameinfo are preferred over older utilities. Non-blocking and asynchronous I/O can be achieved with select, WSAEventSelect, or overlapped I/O using WSASend/WSARecv and completion ports.

Portability and usage: Winsock abstracts Windows networking and supports both IPv4 and IPv6. Applications link against Ws2_32.lib and run on Windows platforms with Winsock support. The API remains a foundational component for network-enabled Windows applications and services.